Thanks, everyone. I’ll stick to that. Got to thank who mantains the nouveau drivers as well!
I also removed these from /etc/environment, because the windows and buttons were glitching a bit. Now it’s fine.
It must be noted that now, at least so far, the mouse pointer doesn’t seem to lag anymore! (it lagged in the beginning, even on the live USB; I see someone is having the same issue here).
Maybe it’s the fact that I installed xorg-x11-drv-nouveau… but shouldn’t it be preistalled?